In the production process of semiconductor elements, liquid crystal elements and the like, miniaturization of patterns formed using lithographic techniques is being undertaken rapidly. To form miniaturized patterns, it is an option to employ a shorter wavelength for irradiation.
In recent years, lithographic techniques using KrF excimer laser beams (wavelength: 248 nm) have been introduced, and lithographic techniques involving ArF excimer laser beams (wavelength: 193 nm) with an even shorter wavelength and EUV rays (wavelength: 13.5 nm) have also been studied.
In addition, as for resist compositions to be used preferably in response to shorter wavelengths of irradiation light and miniaturized patterns, so-called chemically amplified resist compositions, which contain photoacid generators and polymers capable of dissolving in alkaline solutions after acid-leaving groups are removed by the action of acid, have been proposed and their further development and improvement are in progress.
Acrylic polymers having properties of transparency to light with a wavelength of 193 nm are notable for polymers in chemically amplified resist compositions used in ArF excimer laser lithography.
In addition, methods for producing polymer compounds by reversible addition-fragmentation chain transfer (RAFT) are gathering attention. A method using RAFT is a type of living radical polymerization method. In RAFT methods, a compound capable of causing reversible addition-fragmentation chain transfer reactions is used as a chain transfer agent (hereinafter referred to as a RAFT agent), and polymers with a remarkably narrow molecular-weight distribution range are obtained. For example, patent publications 1 and 2 below describe inventions relating to methods for synthesizing polymer compounds using various thiocarbonylthio compounds as RAFT agents.
Also, patent publication 3 describes an invention relating to a method for synthesizing a polymer using a RAFT agent, isolating the polymer, and then removing the RAFT agent remaining at an end of the polymer.